afs: Handle reading past the end of a file

... except that this change doesn't actually handle this, it just
stops clang from throwing an error about the bogus code that's already
in there. This needs fixed properly ...

Reviewed-on: http://gerrit.openafs.org/7090
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 3198cef8ccf0d9cb9a7479c0b973e604e21e62fc)

This change differs slightly from the one on master because on master,
afs_MemRead and afs_UFSRead were consolidated into afs_read().  On the
1.6 branch, we must patch the two functions separately.

Change-Id: I7d8d104c89355c0a3294372340af0e02ab170b59
Reviewed-on: http://gerrit.openafs.org/10744
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>